Method of depositing a thermoplastic polymer in semiconductor fabrication

ABSTRACT

A method of applying a dispersion (which may be in the form of a paste) of particles of a thermoplastic polymer in a liquid medium (i.e., liquid carrier) onto semiconductor wafers, dies, lead frames, and printed circuit boards, for example, to form bonding layers, pads, and bumps, etc.

FIELD OF THE INVENTION

[0001] The present invention relates to semiconductor fabrication.Specifically, it relates to a process of forming protective coatings,adhesive layers, bonding layers, pads, and bumps for die attachmentapplications as well as board level packaging using a dispersion of athermoplastic polymer.

BACKGROUND OF THE INVENTION

[0002] Semiconductor packaging involves a variety of processes thatrequire the formation of protective coatings, adhesive layers, bondinglayers, pads, and bumps for die attachment applications as well as boardlevel packaging. For example, in semiconductor packaging, a singlesemiconductor die is typically mounted within a sealed package. Ingeneral, the package protects the die from damage and from contaminantsin the surrounding atmosphere. The package also provides a system forconnecting the electrical devices formed on the die to a printed circuitboard or other external circuitry.

[0003] The packaging process involves adapting a leadframe (i.e., ametal frame which supports several dies for packaging and provides theleads for the final semiconductor package) to mount severalsemiconductor dice. Each die has a lower surface (i.e., the back of thedie) that is devoid of circuitry, and an upper surface (i.e., the faceof the die) having integrated circuitry constructed thereon. Theintegrated circuitry is electrically accessible via bonding pads whichmay be arranged in a variety of configurations on the face or edges ofthe die. During conventional packaging processes, each die is attachedto a mounting paddle of the leadframe by an adhesive layer. Adhesiveswhich have been used for this include epoxy, acrylic, silicone, andpolyimide materials which are sandwiched between the bottom of the dieand the mounting paddle.

[0004] During the packaging process, the bond pads formed on the die areelectrically connected to the leads of the leadframe using fine bondwires. Following the application of a polyimide protective layer to theface of the die, it, and a portion of the leadframe to which it isattached, is encapsulated in a plastic material, as are all otherdie/leadframe assemblies on the leadframe strip.

[0005] After encapsulation, a trim and form operation separates theresultant interconnected packages and bends the leads of each packageinto the proper configuration. There is a need in the art for improvedmethods of attaching semiconductor dies to leadframes and for attachingdies to a printed circuit board.

[0006] Recent advances in semiconductor manufacture have lead to highercircuit densities and improved packaging technologies. Some high densitycircuits use a lead-on-chip (LOC) packaging technology. In general, anLOC die is formed without a mounting paddle for the die. The leadfingers of the leadframe not only electrically attach to the bond padsvia the bond wires but also adhere to the face of the die and support itduring the encapsulation process. Polymers typically are used as theadhesive for the die and for the necessary structural support.

[0007] In addition to the attachment of leads, there is the attachmentof dies to printed circuit boards. Chip-on-board (COB) is a termreferring to the direct attachment of bare chips onto printed circuitboards (PCBs) by die attach, tape automated bonding (TAB), or flip chipmethods. TAB is a technique which allows automation of the bonding ofone end of a lead to a semiconductor chip and the other end directly toa printed circuit board. TAB is characterized by formation of aconductive bonding projection or “bump” between the chip and the lead.The bump provides the necessary bonding as well as a physical standoff,which prevents lead/chip shorting. Typically the bumps comprise metals,such as gold alloys.

[0008] For flip chip applications, one or more beads of solder (i.e., abump) are applied to the surface of a die (i.e., that surface havingelectronic circuitry) and the chip is then flipped over onto the surfaceof a PCB. Interspersed between bumps is underfill material designed toseal the area between the die and the PCB. Bump dams are also used onflip chips to prevent solder flow and electrical shorting.

[0009] Solder paste is a common interconnecting material for packagingapplications. Solder paste is a mixture of fusible metal powder, fluxes,activators, solvents, binders, etc. Solder paste is thick and tacky,allowing parts to be held in position without additional adhesivesbefore permanent electrically conductive bonds are formed in the solderreflow process. Typically, solder is delivered to the surface in adesired pattern by screen printing and metal stencil printing. The useof solder paste can be undesirable because the surface can be difficultto clean and because of the presence of heavy metals, such as lead, inthe solder.

[0010] Other materials used for attaching and electrically connectingparts in semiconductor fabrication, particularly semiconductorpackaging, include heat activated adhesive tapes, thermoset adhesives(typically cured after delivery to the surface), and solutions ofthermoplastic adhesives.

[0011] Adhesive tapes are cut to desired sizes and shapes and applied toa surface. For example, U.S. Pat. No. 4,906,314 (Farnworth et al)describes a method of die attach wherein a polymer coated tape isapplied to a surface and heat activated. This method is limited to theshapes and sizes which can be cut from such tape.

[0012] Adhesives can also be applied by printing methods (e.g., screenprinting and stencil printing). For example, U.S. Pat. No. 5,220,724(Gerstner) describes the use of a reworkable thermoplastic adhesive tomount surface-mounted devices on a substrate. The adhesive is warmed tomake it fluid and is applied to a surface by screen printing. U.S. Pat.No. 5,286,679 (Farnworth, et al) describes a method of attaching a dieto the lead fingers of a leadframe using either thermoplastic orthermoset adhesive. The adhesive is dried (if thermoplastic) or cured(if thermoset) after application. The adhesive layer is patterned by hotor cold screen printing, by photopatterning a photosensitive adhesive,or by utilizing a resist method of etch back. However, with thesemethods, adhesive application can be difficult because the properviscosity and rheology of the liquid adhesive must be maintained in anarrow range to work properly. In addition, the thickness of theadhesive layer (followed by curing) can be undesirably low for someapplications.

[0013] Thus, there is also a need for improved methods of formingadhesive layers, bumps, and pads on the surface of dies, leadframes, andprinted circuit boards. There is also a need in the art to convenientlydeposit materials by screen or stencil printing in semiconductorpackaging applications, where such materials would not damage the screenor reduce its working life. There is also a need to develop reliablebonding materials which provide good performance properties as well asexhibit economical processing features.

SUMMARY OF THE INVENTION

[0014] The present invention provides a method of applying a dispersion(which may be in the form of a paste) of particles of a thermoplasticpolymer in a liquid medium (i.e., liquid carrier) onto semiconductorwafers, dies, lead frames, and printed circuit boards, for example, toform bonding layers, pads, and bumps, etc. The method of the presentinvention is useful in applications such as surface mount attachment ofdevices to printed circuit boards, chip-on-board (COB), lead on chip(LOC), direct chip attach (DCA), and ball grid arrays (BGA).

[0015] The method of the present invention preferably involves applyinga dispersion of a thermoplastic polymer, such as a polyimide, using aprinting method such as screen printing or stenciling. Typically, themethod of the present invention does not use solvents that can adverselyaffect the screen. Rather, preferred liquid carriers include low boilingsolvents such as water or alcohol. The method of the present inventionis particularly advantageous because these liquid carriers can involvefewer environmental concerns. Further, the working life of thedispersion used in screen printing is increased because thethermoplastic polymer does not cure as the solvent evaporates.

[0016] Using a dispersion of a thermoplastic polymer, screen cleaningfrequencies are also reduced because the dispersion is not sticky andsmearable, therefore the screens are easier to clean. Furthermore, themethod of the present invention allows for the application of moreconsistent coating weights than are possible using conventional methods.This method also allows for a higher throughput and therefore betterefficiency and economy in producing semiconductor packages, for example.

[0017] In another aspect, the method of this invention comprisesapplying a thermoplastic polymer to a leadframe comprising lead fingersby applying a thermoplastic dispersion to the lead fingers, and dryingthe thermoplastic dispersion.

[0018] In another aspect, the method of this invention comprisesattaching a die to a leadframe, the leadframe comprising lead fingers,applying a thermoplastic dispersion to the lead fingers; drying thethermoplastic dispersion; heating the thermoplastic dispersion to form athermoplastic bonding layer, and placing a die against the bondinglayer, thereby attaching the die to the leadframe.

[0019] In another aspect, the method of this invention comprisesapplying a thermoplastic polymer to a printed circuit board by applyinga thermoplastic dispersion in a predetermined pattern to a printedcircuit board, and drying the thermoplastic dispersion.

[0020] In another aspect, the method of this invention comprisesattaching a die to a printed circuit board, by applying a thermoplasticdispersion in a predetermined pattern to a printed circuit board toproduce an area to accept a die; drying the thermoplastic dispersion;heating the thermoplastic dispersion to form a thermoplastic bondinglayer, and placing die against the bonding layer, thereby attaching thedie to the printed circuit board.

[0021] In another aspect, the method of this invention comprises sealinga flip chip on a printed circuit board, the flip chip comprising aplurality of conductive bumps, by placing a flip chip on a printedcircuit board, thus forming voids; applying a thermoplastic dispersionto the voids; drying the thermoplastic dispersion; heating thethermoplastic dispersion to form a thermoplastic underfill material,thereby sealing the flip chip to the printed circuit board.

[0022] In another aspect, the method of this invention comprisesapplying a thermoplastic polymer to a flip chip, the flip chipcomprising a plurality of conductive bumps and spaces between the bumps,by applying a thermoplastic dispersion in the spaces between the bumps,and drying the thermoplastic dispersion.

[0023] In another aspect, the method of this invention comprises makingthermoplastic bump dams on a flip chip, the flip chip comprising aplurality of conductive bumps and spaces between the bumps, by applyinga thermoplastic dispersion in the spaces between the bumps, and dryingthe thermoplastic dispersion; and heating the thermoplastic dispersionto form thermoplastic bump dams.

[0024] In another aspect, the method of this invention comprises makingan array (e.g., a ball grid array), the array comprising a plurality ofconductive thermoplastic deposits on the surface of a substrate of anintegrated circuit package, by applying a thermoplastic dispersion toform deposits; drying the thermoplastic dispersion, and heating thethermoplastic dispersion to form conductive thermoplastic deposits(e.g., bumps, piles, etc.).

[0025] In another aspect, this invention comprises a semiconductorcomponent (such as those described above) having applied thereon adispersion comprising thermoplastic particles and a liquid medium.

[0026] In another aspect, this invention comprises a leadframecomprising lead fingers having applied thereon a dispersion comprisingthermoplastic particles and a liquid medium.

[0027] In another aspect, this invention comprises a printed circuitboard having applied thereon a dispersion comprising thermoplasticparticles and a liquid medium.

[0028] In another aspect, this invention comprises a flip chipcomprising a plurality of conductive bumps and spaces between the bumps,having applied thereon a thermoplastic dispersion in the spaces betweenthe bumps.

[0029] In another aspect, this invention comprises a flip chip mountedon a printed circuit board having voids between the flip chip and theprinted circuit board, having applied to the voids a dispersioncomprising thermoplastic particles and a liquid medium.

[0030] In another aspect, this invention comprises an integrated circuitpackage molded body having applied thereon a dispersion comprisingthermoplastic particles and a liquid medium.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is an illustrative diagram showing a device mounted on aprinted circuit board.

[0032]FIG. 2 is an illustrative diagram showing a cross section of asemiconductor substrate assembly coated with a patterned bonding layerin accordance with the method of the present invention.

[0033]FIG. 3 is an illustrative diagram showing a metal leadframe with abonding layer on the lead fingers, as shown further in cross section inFIG. 3A.

[0034]FIG. 4 is an illustrative diagram showing attachment of leadfingers and bond wires to a single semiconductor die.

[0035]FIG. 5 is an illustrative diagram showing a die attached to aprinted circuit board.

[0036]FIG. 6 is an illustrative diagram showing non-conductive flip chipunderfill material and conductive flip chip bumps on a printed circuitboard.

[0037]FIG. 7 is an illustrative diagram showing conductive bumps on aflip chip.

[0038]FIG. 8 is an illustrative diagram showing a ball grid array on anintegrated circuit.

[0039]FIG. 9 is an illustrative diagram showing a protective coatingover a die attached to a printed circuit board.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0040] The present invention provides a method of applying athermoplastic polymer in the form of a dispersion in a desired patternon semiconductor components. In this application, “semiconductorcomponents” refers to semiconductor substrates or substrate assemblies,including any of the layers or structures thereon, such as dice, leadframes, lead fingers, wire bonds, printed circuit boards, and surfacemount devices. Thus, the term “semiconductor component” includesprotective coatings, bonding layers (e.g., die attach adhesive), bumps,pads (e.g., for wire bonding), and ball grid arrays in varioussemiconductor fabrication applications, particularly semiconductorpackaging applications.

[0041] The method of the present invention is particularly well suitedfor applying structures on a surface of a semiconductor substrate suchas a silicon wafer used in forming integrated circuits. Further, it isparticularly well suited for applying structures in a desiredarrangement and in desired locations (i.e., in a predetermined pattern)on a semiconductor substrate. It is to be understood that the method ofthe present invention is not limited to deposition on silicon wafers;rather, other types of materials (e.g., gallium arsenide, ceramic, etc.)can be used as well. If the substrate is a semiconductor wafer, thethermoplastic polymer can be applied directly on the bare surface of thewafer, or it can be formed on any of a variety of the layers (i.e.,surfaces) in a patterned wafer, for example.

[0042] In the present invention, a stable dispersion of thermoplasticparticles in a liquid medium is applied in a desired pattern. Afterdeposition, the article is dried to remove the liquid medium. This canbe done simply by allowing the liquid medium (i.e., liquid carrier) toevaporate at room temperature, or by applying heat or a vacuum to driveoff the liquid medium. The article can be heated sufficiently to meltthe thermoplastic particles, depending on the application anddesirability for such. The deposited and dried dispersion, which may beconductive or nonconductive, is useful as various structures on thesemiconductor components.

[0043] The term “dispersion” as used herein refers to a stablesuspension of finely divided thermoplastic particles in a liquid medium.The thermoplastic particles are substantially insoluble in the fluidmedium. The thermoplastic particles also are substantially polymerizedor crosslinked before formation of the dispersion. That is, no furtherreaction of the polymer (other than fusing or melting to form a film,for example,) occurs after the dispersion is coated and/or dried orheated. The particles in the dispersion preferably are less than about250 microns in diameter. More preferably, the particles range in sizefrom about 3 microns to about 250 microns.

[0044] In a stable dispersion (i.e., suspension), the particles do notsettle out of the liquid medium rapidly. That is, they generally remainin suspension for a sufficient amount of time to apply the dispersion tothe desired substrate. To be useful for most applications, whichtypically involve screen printing or stenciling, the dispersions arepreferably stable for a period of at least about 48 hours at 25° C., andmore preferably, for about 1 year at −40° C.

[0045] A stable dispersion is typically also not readily filterable toremove the particles. The solids content of the dispersion is preferablyat least about 20 percent solids by weight, and more preferably, atleast about 50 percent solids by weight, and most preferably, at leastabout 95 percent solids by weight, based on the total weight of thedispersion.

[0046] The viscosity of the dispersion of particles of a thermoplasticpolymer in a liquid medium (i.e., the thermoplastic dispersion) ispreferably such that the dispersion can be conveniently applied bypattern coating techniques. More preferably, the viscosity of thedispersion ranges from about 10,000 centipoise at 25° C. to about300,000,000 centipoise at 25° C. In particularly preferred embodiments,the dispersion is thick, similar to a paste.

[0047] “Thermoplastic” polymers soften when exposed to heat and returnto their original condition when cooled to room temperature. Naturalsubstances that exhibit this behavior are crude rubber and a number ofwaxes; however, the term is usually applied to synthetics such aspolyvinyl chloride, nylon, fluorocarbons, linear polyethylene,polyurethane prepolymer, polystyrene, polypropylene, and cellulosic andacrylic resins. This is distinct from “thermoset” polymers, which cureor “set” upon heating, and cannot be returned to a plastic state byheating. Thermoplastic polymers are commercially available in variousforms, such as powders and pellets. They can be elastomeric. “Elastomer”is a term referring to polymers having properties similar to those ofvulcanized natural rubber, namely the ability to be stretched to atleast twice their original length and to retract very rapidly toapproximately their original length when released. The term includesuncrosslinked polyolefins that are thermoplastic; these are referred toas thermoplastic olefin rubbers. The thermoplastic polymer may alsocontain unreacted monomeric components and other materials which do notadversely affect the properties of the final dried thermoplasticpolymer.

[0048] Suitable thermoplastic polymers for use in the method of thepresent invention include high and low density polyethylene,ethylene/vinylacetate copolymer (EVA), polypropylene, polystyrene,acrylonitrile-butadiene-sytrene (ABS), poly(vinyl butyral) (PVB),poly(vinyl chloride (PVC), polyimide, polyamide, poly(methylmethacrylate), poly(ethylene terephthalate), and cellulose acetate.

[0049] A preferred thermoplastic polymer for the practice of the presentinvention is a polyimide. Polyimides are generally prepared in a polarsolvent, such as N-methyl pyrrolidone, at room temperature, by theaddition of a dianhydride to a solution of a diamine (such as poly(amicacid)) and allowed to stir for several hours under moisture-freeconditions. This solution is cured (i.e., fully reacted) and made intothe desired form. Finely divided fully imidized polymer suitable forpractice in the present invention include polyimide particlescommercially available from Dexter Composites of Cleveland, Ohio, as“M100.”

[0050] In a more preferred embodiment of the present invention, thepolyimide contains siloxane functionality (a class of compounds having aSi—O—Si bond) as is known in the art. Siloxane is incorporated into thepolyimide by reacting siloxane-containing compounds with poly(amic acid)to form poly(imide siloxane). Siloxanes are known to alter theproperties (e.g., flow, compliance, modulus) of the polyimides. Forexample, at low siloxane content (about 10% by weight), a poly(imidesiloxane) is rigid and more like a polyimide. As the siloxane contentincreases, flexibility also increases. At levels above about 40%siloxane, siloxane is the continuous phase and the materials arecharacterized as thermoplastic elastomers.

[0051] The liquid medium can be any liquid suitable for making adispersion of particles of the thermoplastic polymers. Preferably, suchliquids not only make stable suspensions, but also do not adverselyaffect the printing apparatus (such as the screen for screen printing),and they also evaporate at low temperatures (i.e., up to about 200° C.).Suitable liquid media include, for example, water, organic solvents, andliquid thermoset components. Preferably, the liquid media include one ormore low boiling solvents (i.e., those having a boiling point of nogreater than about 200° C.). More preferably, the liquid media includewater and alcohols. Although water and organic solvents are desired, andlow boiling solvents are preferred, the liquid medium may also includemonomers and/or polymers such as those in a liquid thermoset compositionin amounts up to about 50 percent of the thermoplastic particles. Ifpresent in the dispersion, the liquid thermoset composition cures uponheating. The presence of the liquid thermoset can be advantageous inproducing better adhesion of the thermoplastic dispersion to asubstrate.

[0052] The dispersion of the present invention may also include fillerparticles in the form of powders, flakes, and fibers. Fillers can beadded to adjust viscosity or to provide desirable properties to thedispersion and/or resultant coating, such as conductivity, color,opacity, etc. Fillers include such materials as particles of polymers,intermetallics, metals (including metalloids), and metal compounds(including metalloid compounds such as silicon carbide and silica).Fillers can be added to impart electrical conductivity (e.g. silver,aluminum, iron, nickel, graphite and metal-coated particles ofnon-conductive materials) or to impart thermal conductivity withoutelectrical conductivity (e.g., aluminum nitride, alumina, and boronnitride). The amount of filler can range from about 1 percent by weightto about 85 percent by weight. For applications in which an electricalconnection is made, high percentages of filler are used; whereas foradhesive applications, low percentages typically are used.

[0053] Other additives can be incorporated into the dispersions of thepresent invention. Such additives can be added during the preparation ofthe dispersion just prior to application. Alternatively, additivescommonly incorporated in commercially available thermoplastic materialscan be incorporated into the dispersions. However they are added,additives include antistatic agents, colorants, flame retardants,lubricants, plasticisers, and stabilizers.

[0054] To prepare the dispersion, thermoplastic particles in the desiredsize range are mixed together with the liquid medium by stirring.Fillers and/or other additives can be similarly added.

[0055] The dispersion can be applied by a wide variety of methods,particularly a pattern coating technique, such as mesh screen printing,metal stencil printing, pneumatic dot dispensing, positive displacementdispensing, or pin transfer techniques.

[0056] The dispersion can be applied in a desired pattern by thesetechniques to areas on a semiconductor wafer or die, printed circuitboard, lead frames, and other substrates in a predetermined pattern.“Predetermined pattern” refers to a desired arrangement of areas havingapplied thereon the dispersion of this invention. For example, on asemiconductor wafer (which may have electronic circuitry thereon), apredetermined pattern is one in which there are uncoated areas and areascoated with the thermoplastic dispersion.

[0057] Preferred methods of applying the thermoplastic dispersioninclude screen printing and stencil printing. In screen printing, thereis a means for mounting a patterned screen, a means for bringing anarticle to be printed into registration with the pattern on the screen,and a means for forcing material through the screen onto the article tobe printed. Screens typically are fabricated from stainless steel,polyester, or nickel and have openings ranging in size from about 2.5microns (0.1 mil) to about 12.7 millimeters (500 mils). Preferably, thescreen printing apparatus is capable of repeatedly positioning thearticle to be printed in registration with the pattern on the screen toa resolution of approximately 10 microns. An advantage to the presentinvention is that no preparation of the screen is required beforeprinting. That is, it does not need to be coated or treated and it canbe used repeatedly because the dispersion does not clog up the screen.

[0058] In stencil printing, a pattern is formed on the surface of asubstrate by forcing the thermoplastic dispersion through a templatecontaining openings in the shape of the desired pattern. Stencilstypically have larger openings than screens, although these terms areoften used interchangeably. The template is placed over the surface ofthe substrate on which the pattern is to be formed and the dispersion isforced through the template by a squeegee blade or other means.

[0059] After application of the thermoplastic dispersion in the desiredpattern, the patterned article is dried and/or heated to remove theliquid medium. The article is typically first dried at room temperature(typically about 25° C. to about 30° C.). If so desired, thethermoplastic particles can then be heated. The temperature at which thedispersion or dried polymer particles are heated is sufficient to causemelting of the particles and fusing into a uniform film. Preferably, thedispersion or dried particles are exposed to a temperature of no greaterthan about 500° C., for a time sufficient to melt the particles. Thethermoplastic particles melt to produce consistent, reproducible, goodquality films in the printed regions.

[0060] The preferred method for depositing a patterned layer of thethermoplastic dispersion is stencil printing. The preferred method fordepositing bump dams is stencil printing. To deposit the thermoplasticdispersion in the shape of balls, useful for ball grid arrays, stencilprinting, dot dispensing, positive displacement printing and pintransfer techniques can also be used to deposit balls. Pin transfertechniques can be used to deposit line patterns.

[0061] The method of the present invention produces structures onsemiconductor components such as protective coatings, bonding layers,pads, bumps, and ball grid arrays for semiconductor fabrication,particularly semiconductor packaging, applications. These structures maybe conductive or nonconductive, depending upon the desired application.

[0062] The method of the present invention is particularly useful formounting electronic components (e.g., surface mount resistors,capacitors, integrated circuits, diodes) to printed circuit boards. Thismethod is useful in lead-on-chip (LOC) applications (e.g., bonding ofleads to chips and leadframes), chip on board (COB) applications (e.g.,die attach adhesives, wire bonding, tape automated bonding (TAB)), andfor use in making flip chip conductive bumps, flip chip underfill, bumpdam material, and ball grid array bumps. The method of the presentinvention can be used to produce the articles illustrated in the Figuresand described below, but is not limited to these illustrations.

[0063] Referring now to FIG. 1, a device (e.g., a resistor, a capacitor,an integrated circuit, or a diode which is designed to be surfacemounted) 10, having solder terminations 12, is mounted on a printedcircuit board 14 by nonconductive thermoplastic bonding layer 15.Nonconductive thermoplastic bonding layer 15 holds device 10 in placefor subsequent processing (e.g., solder reflow). Solder 16 makeselectrical connection with PCB circuit trace 18. Nonconductive bondinglayer 15 is deposited from the thermoplastic dispersion according tothis invention, preferably using screen printing or stenciling, thendried and heated to form bonding layer 15.

[0064] Referring now to FIG. 2, a cross section of semiconductor wafer20 is shown with a plurality of dice 22, and a plurality of streets 24between dice 22. The thermoplastic dispersion of this invention isdeposited in a desired, predetermined pattern, typically by stencilprinting, then dried and heated to form thermoplastic bonding layer 25.The pattern is such that streets 24 and pad area 26 are free ofthermoplastic bonding material. Thus semiconductor wafer 20 is ready forsaw cutting through streets 24 (referred to as singulation). Pad area 26will be used to make electrical connections during subsequent wirebonding.

[0065] Referring now to FIG. 3, a metal leadframe 30 is shown with drivesprocket holes 32, which facilitate indexing with automated packagingmachinery. Leadframe 30 includes a plurality of generally parallel andspaced lead fingers 34. Lead fingers 34 can be coated by dot dispensingor stencil printing with the thermoplastic dispersion of this invention,which is then dried and heated to form a nonconductive thermoplasticbonding layer 37. Lead fingers 34 are shown further in cross section(taken along line A-A) in FIG. 3A. Thermoplastic bonding layer 37 isapplied according to the method of the present invention. A die (notshown) will be positioned on leadframe 30 during manufacture and held inplace by bonding layer 37 on lead fingers 34. After the die is in place,electrical connection will occur by means of wire bonds.

[0066] Referring now to FIG. 4, wire 40 is attached to lead finger 42and conductive (metal) bond pad 44 by, for example, thermocompressionbonding. Lead finger 42 is held in place on die 46 by means ofnonconductive thermoplastic bonding layer 45. The thermoplasticdispersion of this invention is deposited, typically by screen printing,in desired areas on the die, then dried and heated to form bonding layer45.

[0067] Referring now to FIG. 5, die 50 is shown attached to printedcircuit board 52 by means of conductive die attach thermoplastic bondinglayer 53. A thermoplastic dispersion having conductive filler therein isapplied to printed circuit board 52, typically by screen printing, in adesired, predetermined pattern. The dispersion is dried and heated toform thermoplastic bonding layer 53. Die 50 is placed onto thermoplasticbonding layer 53. Wire bond 54 connects the surface of die 50 to circuittrace 56 on printed circuit board 52.

[0068] Referring now to FIG. 6, there is integrated circuitry (notshown) on the surface of chip 60 which is facing printed circuit board62. Chip 60 on board 62 is shown in cross section. Chip 60 is held inplace by means of a plurality of conductive flip chip bumps 64 thusforming voids between chip 60 and printed circuit board 62. Thethermoplastic dispersion of this invention is applied to the voids,dried, and heated, to form thermoplastic nonconductive flip chipunderfill material 66. Underfill material 66 serves to seal the areabetween chip 60 and printed circuit board 62. Flip chip bumps 64 can bemade of solder or can be deposited from the thermoplastic dispersion ofthis invention by dot dispensing, pin transfer techniques and stencilprinting methods, then drying and heating to form bumps 64.

[0069] Referring now to FIG. 7, the surface of a flip chip 70 is shownwith conductive bumps 72 distributed about the edges of chip 70. FIG. 7Ashows flip chip 70 in cross section taken along A-A. Flip chip 70 has aplurality of conductive bumps 72 interspersed with a plurality ofnon-conductive bump dams or bonding layer 74. Conductive bumps 72 makeelectrical connection between the chip and the next layer of circuitry.Conductive bumps 72 may comprise solder or conductive thermoplasticmaterials applied from the thermoplastic dispersion of this invention.Non-conductive bump dams or bonding layer 74 are formed by firstapplying the thermoplastic dispersion of this invention in the spacesbetween the conductive bumps, then drying and heating to form bump dams74. Bump dams 74 provide stand-off from the board and prohibit solderflow (when conductive bumps comprise solder) from reaching adjacentbumps.

[0070] Referring now to FIG. 8, a plurality of conductive thermoplasticballs 82 makes up ball grid array 80 on surface 84 of an integratedcircuit package. A thermoplastic dispersion having conductive fillertherein is first used to deposit balls of dispersion on surface 84. Theballs on surface 84 can be formed by stencil printing. The thermoplasticdispersion is dried to remove the liquid medium, and then heated to forma plurality of conductive thermoplastic balls 82. Ball grid array 80 onthe integrated circuit package is then ready to be mounted on a circuitboard (the conductive balls making contact with the circuit board).

[0071] Referring now to FIG. 9, die 90 is shown attached to printedcircuit board 92 by means of conductive die attach layer 93. Wire bond94 connects the surface of die 90 to circuit trace 96 on printed circuitboard 92. A layer of thermoplastic dispersion is applied to cover thedie and wire bonds, then dried and heated to form protective coating 95.Protective coating 95 encapsulates die 90 and bonding wire 94, thusprotecting them from damage.

[0072] Although the invention has been described above with particularreference to various embodiments thereof, variations and modificationsof the present invention can be made within a contemplated scope of thefollowing claims.

[0073] The foregoing detailed description has been given for clarity ofunderstanding only. No unnecessary limitations are to be understoodtherefrom. The invention is not limited to the exact details shown anddescribed, for variations obvious to one skilled in the art will beincluded within the invention defined by the claims. The completedisclosures of all patents, patent documents, and publications listedherein are incorporated by reference, as if each were individuallyincorporated by reference.

What is claimed is:
 1. A method of applying a thermoplastic polymer to asemiconductor component comprising: providing a dispersion comprisingthermoplastic particles and a liquid medium; applying the dispersion onthe surface of the semiconductor component; drying the dispersion. 2.The method of claim 1 further including a step of applying heat to thedispersion to form a thermoplastic structure.
 3. The method of claim 1wherein the step of depositing occurs by screen printing.
 4. The methodof claim 1 wherein the step of depositing occurs by stencil printing. 5.The method of claim 1 wherein the step of depositing occurs in apredetermined pattern.
 6. The method of claim 1 wherein thethermoplastic particles comprise polyimide particles.
 7. The method ofclaim 6 wherein the polyimide is a poly(siloxane)imide.
 8. The method ofclaim 1 wherein the liquid medium is a low boiling solvent.
 9. Themethod of claim 1 wherein the liquid medium is selected from the groupof water and alcohol.
 10. A method of applying a thermoplastic polymerto a leadframe, the leadframe comprising lead fingers, the methodcomprising: applying a thermoplastic dispersion to the lead fingers; anddrying the thermoplastic dispersion.
 11. A method of attaching a die toa leadframe, the leadframe comprising lead fingers, the methodcomprising: applying a thermoplastic dispersion to the lead fingers;drying the thermoplastic dispersion; heating the thermoplasticdispersion to form a thermoplastic bonding layer; placing a die againstthe bonding layer, thereby attaching the die to the leadframe.
 12. Amethod of applying a thermoplastic polymer to a printed circuit board,the method comprising: applying a thermoplastic dispersion in apredetermined pattern to a printed circuit board; and drying thethermoplastic dispersion.
 13. A method of attaching a die to a printedcircuit board, the method comprising: applying a thermoplasticdispersion in a predetermined pattern to a printed circuit board toproduce an area to accept a die; drying the thermoplastic dispersion;heating the thermoplastic dispersion to form a thermoplastic bondinglayer; and placing die against the bonding layer, thereby attaching thedie to the printed circuit board.
 14. A method of sealing a flip chip ona printed circuit board, the flip chip comprising a plurality ofconductive bumps, said method comprising: placing a flip chip on aprinted circuit board, thus forming voids; applying a thermoplasticdispersion to the voids; drying the thermoplastic dispersion; heatingthe thermoplastic dispersion to form a thermoplastic underfill material;thereby sealing the flip chip to the printed circuit board.
 15. A methodof applying a thermoplastic polymer to a flip chip, the flip chipcomprising a plurality of conductive bumps and spaces between the bumps,the method comprising: applying a thermoplastic dispersion in the spacesbetween the bumps; and drying the thermoplastic dispersion.
 16. A methodof making thermoplastic bump dams on a flip chip, the flip chipcomprising a plurality of conductive bumps and spaces between the bumps,the method comprising: applying a thermoplastic dispersion in the spacesbetween the bumps; and drying the thermoplastic dispersion; and heatingthe thermoplastic dispersion to form thermoplastic bump dams.
 17. Amethod of making an array, the array comprising a plurality ofconductive thermoplastic deposits on the surface of a molded body of anintegrated circuit package, the method comprising: applying athermoplastic dispersion to form deposits; drying the thermoplasticdispersion; and heating the thermoplastic dispersion to form aconductive thermoplastic deposits.
 18. A semiconductor component havingapplied thereon a dispersion comprising thermoplastic particles and aliquid medium.
 19. A leadframe comprising lead fingers having appliedthereon a dispersion comprising thermoplastic particles and a liquidmedium.
 20. A printed circuit board having applied thereon a dispersioncomprising thermoplastic particles and a liquid medium.
 21. A flip chipcomprising a plurality of conductive bumps and spaces between the bumps,having applied thereon a thermoplastic dispersion in the spaces betweenthe bumps.
 22. A flip chip mounted on a printed circuit board havingvoids between the flip chip and the printed circuit board, havingapplied to the voids a dispersion comprising thermoplastic particles anda liquid medium.
 23. An integrated circuit package molded body havingapplied thereon a a dispersion comprising thermoplastic particles and aliquid medium.
 24. A method of applying a thermoplastic polymer to asemiconductor component comprising: providing a dispersion comprisingthermoplastic particles and a liquid medium; applying the dispersion onthe surface of the semiconductor component; and removing the liquidmedium.
 25. The method of claim 24 further including a step of applyingheat to the thermoplastic particles to form a thermoplastic structure.26. The method of claim 24 wherein the dispersion further comprises afiller.
 27. The method of claim 24 wherein the dispersion furthercomprises liquid thermoset components.
 28. The method of claim 24wherein the thermoplastic particles are elastomeric.
 29. The method ofclaim 24 wherein the thermoplastic particles comprise thermoplasticolefin rubber particles.
 30. The method of claim 24 wherein thethermoplastic particles comprise a polymer selected from the groupconsisting of polyethylene, ethylene/vinylacetate, polypropylene,polystyrene, acrylonitrile-butadiene-styrene, poly(vinyl butyral),poly(vinyl chloride), polyimide, polyamide, poly(methyl methacrylate),poly(ethylene terephthalate), and cellulose acetate.
 31. The method ofclaim 24 wherein the liquid medium is selected from the group consistingof water, organic solvents, and liquid thermoset components.
 32. Themethod of claim 31 wherein the liquid medium is selected from the groupconsisting of water and alcohol.
 33. A method of applying athermoplastic polymer to a leadframe, the leadframe comprising leadfingers, the method comprising: applying a thermoplastic dispersioncomprising thermoplastic particles and a liquid medium to the leadfingers; and removing the liquid medium.
 34. A method of attaching a dieto a leadframe, the leadframe comprising lead fingers, the methodcomprising: applying a thermoplastic dispersion comprising thermoplasticparticles and a liquid medium to the lead fingers; removing the liquidmedium; heating the thermoplastic particles to form a thermoplasticbonding layer; and placing a die against the bonding layer, therebyattaching the die to the leadframe.
 35. A method of applying athermoplastic polymer to a printed circuit board, the method comprising:applying a thermoplastic dispersion comprising thermoplastic particlesand a liquid medium in a predetermined pattern to a printed circuitboard; and removing the liquid medium.
 36. A method of attaching a dieto a printed circuit board, the method comprising: applying athermoplastic dispersion comprising thermoplastic particles and a liquidmedium in a predetermined pattern to a printed circuit board to producean area to accept a die; removing the liquid medium; heating thethermoplastic particles to form a thermoplastic bonding layer; andplacing the die against the bonding layer thereby attaching the die tothe printed circuit board.
 37. A method of sealing a flip chip on aprinted circuit board, the flip chip comprising a plurality ofconductive bumps, said method comprising: placing a flip chip on aprinted circuit board, thus forming voids; applying a thermoplasticdispersion comprising thermoplastic particles and a liquid medium to thevoids; removing the liquid medium; and heating the thermoplasticparticles to form a thermoplastic underfill material thereby sealing theflip chip to the printed circuit board.
 38. A method of applying athermoplastic polymer to a flip chip, the flip chip comprising aplurality of conductive bumps and spaces between the bumps, the methodcomprising: applying a thermoplastic dispersion comprising thermoplasticparticles and a liquid medium in the spaces between the bumps; andremoving the liquid medium.
 39. A method of making thermoplastic bumpdams on a flip chip, the flip chip comprising a plurality of conductivebumps and spaces between the bumps, the method comprising: applying athermoplastic dispersion comprising thermoplastic particles and a liquidmedium in the spaces between the bumps; removing the liquid medium; andheating the thermoplastic particles to form thermoplastic bump dams. 40.A method of making an array, the array comprising a plurality ofconductive thermoplastic deposits on the surface of a molded body of anintegrated circuit package, the method comprising: applying athermoplastic dispersion comprising thermoplastic particles and a liquidmedium to form deposits; removing the liquid medium; and heating thethermoplastic particles to form conductive thermoplastic deposits.
 41. Amethod of applying a thermoplastic polymer to a semiconductor componentcomprising: providing a dispersion comprising thermoplastic particlesand a liquid medium wherein the thermoplastic particles are less thanabout 250 microns in diameter; applying the dispersion on the surface ofthe semiconductor component; and removing the liquid medium.
 42. Amethod of applying a thermoplastic polymer to a semiconductor componentcomprising: providing a dispersion comprising thermoplastic particlesand a liquid medium; coating the dispersion on the surface of thesemiconductor component; and removing the liquid medium.
 43. Asemiconductor component prepared by the method of claim 24 .
 44. Aleadframe comprising lead fingers prepared by the method of claim 33 .45. A printed circuit board prepared by the method of claim 35 .
 46. Aflip chip comprising a plurality of conductive bumps and spaces betweenthe bumps prepared by the method of claim 38 .
 47. A flip chip mountedon a printed circuit board having voids between the flip chip and theprinted circuit board prepared by the method of claim 37 .